In recent years one has become increasingly aware of the impact of human activities on the environment and the negative consequences this may have. Ways to reduce, reuse and recycle resources are becoming more important. In particular, clean water is becoming a scarce commodity. Therefore, various methods and devices for purifying water have been published.
A method for water ion removal is by capacitive deionisation, using an apparatus provided with a flow through capacitor (FTC) for removal of ions in water. The FTC functions as an electrically regenerable cell for capacitive deionisation. By charging electrodes, ions are removed from an electrolyte and are held in electric double layers at the electrodes. The electrodes can be (partially) electrically regenerated to desorb such previously removed ions without adding chemicals.
The apparatus to remove ions comprises one or more pairs of spaced apart electrodes (a cathode and an anode) and a spacer, separating the electrodes, allowing water to flow between the electrodes. The electrodes may be made from a high surface area electrically conducting material such as activated carbon, carbon black, a carbon aerogel, carbon nano fiber, carbon nano tubes, graphene or one or more mixtures thereof. The electrodes may be placed as a separate layer on top of a current collector or may alternatively be coated directly onto the current collector. A current collector is made from an electrically conductive material and allows the transport of charge in and out of the electrode.
The apparatus has a housing comprising an inlet to let water in the housing and an outlet to let water out of the housing. In the housing, layers of current collectors, electrodes and spacers are stacked in a “sandwich” fashion or spirally wound by a compressive force, normally by mechanical fastening.
A charge barrier may be placed between the electrode and the spacer, the term charge barrier referring to a layer of material, which can hold an electric charge and which is permeable or semi-permeable for ions. Ions with the same charge signs as that in the charge barrier mostly cannot pass the charge barrier. Therefore, ions which are present in the electrode compartment adjacent to the charge barrier and which have the same charge sign as the charge in the charge barrier, are retained or trapped in the electrode compartment. A charge barrier may allow an increase in ion removal efficiency as well as a reduction in the overall energy consumption for ion removal.
U.S. Patent Application Publication No. US 2008/0105551 A1 discloses an energy recovery converter for recovering of energy from a super capacitor desalination cell.